A single phase series motor is also known as a universal motor as it can operate on either AC or DC power. It is a single phase motor with a commutator whose rotor windings are connected in series with stator windings via brushes. Due to its characteristics of high rotating speed, small size, high starting torque, convenient speed regulation and series excitation, the universal motor is commonly used for driving low power appliances that need a high rotating speed, small size and low weight, such as medical devices, power tools, and domestic electric appliances and so on.
A typical known universal motor comprises a stator core which comprises two teeth (stator poles) opposite to each other and two yokes connecting the two teeth at both sides. When the windings are electrified, two magnetic poles with opposite polarity are formed at the stator poles. Traditionally the stator core is formed by stacking a plurality of stator laminations together and each lamination is a monolithic piece with a closing structure. During production, the stator laminations are stacked together to form the stator core firstly, then stator winding are wound on the stator core. It is not convenient to wind windings on a closing structure, so the winding efficiency is low and sometimes the number of turns of the winding is limited.
JP9131003A discloses a motor whose stator core is constituted by assembling a plurality of divided bodies together. During production, the stator windings are wound at the straight parts of the divided bodies firstly, and then the divided bodies with stator windings are assembled together. In this patent application the above mentioned problem is able to be solved. However, the concentricity of the pole arcs of the stator poles can not be assured as undesired position deviation between the pole arcs may generate during the assembly of the divided bodies.
Hence there is a desire for a single phase electric motor with an improved stator structure.